Detailed Characterization of the Surface and Growth Mechanism of Monodisperse NiSn Nanoparticles.

Synthesis of most tin-based bimetallic nanoparticles is a challenging task because of the differences in the redox potential and the melting point between both components. This article presents a co-reduction synthesis of monoclinic NiSn nanoparticles. Varying time and temperature gives the possibility to control the size of the nanoparticles in the range of 4-12 nm. The products were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy measurements. Although the synthesis was conducted entirely oxygen free, the postsynthetic treatment undertaken under air leads to the formation of an amorphous oxide shell. The oxide shell consists of an outer tin-rich region and a nickel-rich region at the interface to the metallic NiSn core. On the basis of the investigation of the particles at different stages of the synthesis, we propose a growth mechanism for the NiSn nanocrystals. These results can be a guidepost for the synthesis of other tin-based bimetallic nanoparticles.